COCKROACHES: Blattodea

PHYSICAL CHARACTERISTICS

Cockroaches are related closely to termites and mantids (such as the praying mantis) and are sometimes grouped with them. Adult cockroaches range in length from 0.8 to 3.1 inches (20.3 to 78.7 millimeters). They are flat and oval in shape, and they usually have four wings. Most species are uniformly dark in color and are typically black, brown, or reddish brown. Some species have unique markings, warning possible predators (PREH-duh-ters), or animals that hunt them for food, that they might be poisonous or taste bad. The larvae (LAR-vee), or cockroach young, look very similar to the adults. While many cockroaches have body chemicals that make them taste bad, most do not. Brightly colored species are mostly mimics, pretending to look like some other kind of insect that predators associate with a bad taste, painful bites, or stings. Some cockroaches that live in the tropics look like fireflies, ladybird beetles, or wasps. Almost nothing is known about the relationship of these cockroaches to the insects they mimic.

Cockroaches have strong, chewing mouthparts that point downward. The threadlike antennae (an-TEH-nee), feelers, are usually longer than the body. Their bodies are made up of many small segments too numerous to count easily. They have compound eyes, eyes with many lenses, but in some species, especially those that live in caves, they may be small or absent. The first part of the thorax is often shieldlike, and the edge often covers most of the head. The forewings, if there are any, are slightly thickened membranes with a network of supporting veins. These wings may be short, exposing part of the abdomen, or long, covering the abdomen entirely. The hind wings, if present, are sometimes fanlike, but they may also be very small. They, too, are somewhat like membranes and thinner, and they have a network of supporting veins. The cockroaches' long and spiny legs are especially suited for running, although some species rely on them for digging.

GEOGRAPHIC RANGE

Cockroaches are found around the world, with most species living in the tropics. Species are found wherever humans live and work.

HABITAT

Wild cockroaches do not live with humans and are not considered pests. They live almost everywhere in the world, except in very cold habitats. However, one species of cockroach, Eupolyphaga everestinia, is found on the slopes of Mount Everest at 18,500 feet (5,639 meters). German cockroaches and other pest species can survive indoors in extremely cold climates. Cockroaches live in caves, mines, animal burrows, bird nests, ant and termite nests, deserts, and even around water. Most species live outdoors and spend their days near the ground, hiding under bark, dead leaves, soil, logs, or stones. About twenty species of cockroaches worldwide have the same temperature and moisture requirements as humans do. They prefer to live in homes, restaurants, food stores, hospitals, and sewers. Living in these stable climates protects them from extremely high or low temperatures and assures them of plenty of water.

Many species live on plants, but it is not clear whether the plants are essential to their survival. Most cockroaches found on plants are simply taking advantage of a place to hide and find food. Some species damage plants by feeding on them, but others transport pollen from one tropical plant to another. Several species prefer to live on land at the edges of streams or pools, and they sometimes spend brief periods of time in the water.

In the western United States, desert cockroaches live on plants during the day and avoid the blistering sun of spring, summer, and fall. From November through March, when the nighttime temperatures are cooler, they burrow into the sand at the bases of plants. They come up to the surface just after dark to feed, taking advantage of the warmest nighttime temperatures.

DIET

Cockroaches eat almost any plant or animal. Some pest species can survive days or weeks without food or water and can live up to three months on just water. Cave-dwelling species will eat bat droppings, while those living in sewers will feed on human waste. Many species that live underground or in dead trees burrow into soil or wood and form a chamber from which they emerge to forage (FOR-ihj), or search, for food. They collect dead leaves and carry them back to the chamber, where they can feed in safety. Species that feed on dead wood depend on microscopic animals or bacteria in their stomachs to help them digest their food.

BEHAVIOR AND REPRODUCTION

Most species are active at night, but some wild cockroaches are active during the day.

Many cockroaches burrow under the ground, beneath dead leaves, or in rotten wood to avoid danger or to rest. Cave-dwelling species burrow into piles of bat waste or slip into narrow cracks in rock walls. Some species run quickly or fly away to avoid danger. Others simply freeze with the approach of a predator. Many cockroaches have special organs in their bodies that make a variety of irritating chemicals that they spray from the tip of the abdomen at their attackers. Many larval cockroaches and some adults produce a glue from the abdomen, which sticks to the legs of ants and beetles, preventing them from attacking the cockroach.

When disturbed, many cockroaches can make sounds. Madagascan hissing cockroaches hiss by quickly blowing air out of breathing holes along the sides of their abdomens. In other species there is a rasp on the edge of the midsection. Next to the rasp is a thickened vein, or file, on the forewing. By rubbing these two structures together, the cockroach can make a faint rasping or squeaking sound.

Some cockroaches live in groups and provide care for their larvae. The rhino cockroach of Queensland, Australia, digs its burrow in sandy soil and builds an underground nest for its young, lining it with leaves, grass, and roots. Other species live in groups but do not care for their young. Still other cockroaches are loners, living mostly by themselves until it is time to mate.

Mates locate each other through pheromones (FEHR-uh-mohns), special chemicals released from the body that are especially attractive to members of the opposite sex of the same species. Eyesight plays little or no part in finding a mate or in courtship, despite the fact that most species have well-developed compound eyes. Many cockroaches engage in complex courtship dances. Females "call" males by raising their wings to expose special glands on the abdomen that release a pheromone to attract the male. Males have their own special organs on their backs that the female either eats or licks during mating. Other species show little or no courting activity before mating. During mating the male transfers his sperm packet directly into the reproductive organs of the female.

Nearly all female cockroaches put their eggs in a pillow-like capsule. Each capsule may have just a few to nearly 250 eggs, aligned in two rows. In some species the female carries the egg capsule on the tip of her abdomen for several days or weeks and then later leaves or buries them near a good supply of food and water. Some species can draw the capsule into the abdomen for short periods of time, to protect it. In other species, the capsule is kept in the abdomen until the eggs hatch inside the mother. The larvae are then "born" as they leave the mother's body. A few Australian cockroaches do not produce an egg capsule, but the eggs are kept inside the body. Only one species, Diploptera punctata, gives birth to live young. Its eggs are kept inside the body without a capsule and are nourished, or fed, by the mother's body until they are born. Most cockroaches never see their young. But in some species the larvae gather in a group under the mother, where they remain for a short period of time. Among some cockroaches the larvae spend their first days in a special chamber under the mother's wings.

COCKROACHES AND PEOPLE

If they are not controlled, some species may build up huge populations not only in homes and businesses but also in sewers. They are known to carry funguses; bacteria; parasitic worms, worms that infest the cockroaches' internal organs; and other microscopic organisms on and in their bodies that cause diseases in humans. They have the potential for spreading harmful organisms indirectly, through contact with foods and utensils used in home and commercial food preparation areas. There is still no solid evidence that cockroaches spread diseases to humans, but they can trigger allergic reactions among people who are especially sensitive to them. Researchers regularly working with cockroaches in laboratories may eventually become sensitive to them. In time they may experience allergy attacks, asthma, or skin irritations when exposed to cockroaches or the materials with which cockroaches have come into contact.

Pest species are often used for experiments and research in university and government laboratories, studying how their bodies work. Researchers are developing tiny "robotic" cockroaches using the Madagascan hissing cockroach as a model. Equipped with wristwatch-sized sensors and a video camera to help start and steer, the "Biobot" cockroach is able to "see" and take measurements in faraway places that are not safe for humans, such as buildings that have been destroyed by bombs or earthquakes.

Most cockroaches do not live with humans and are not considered pests. Instead, these species live in tropical rainforests, mountains, and deserts. They break down plant materials, recycling them into food that can be used by other plants and animals. In parts of Asia, humans eat cockroaches as food. In southern China and in other parts of the world, dried specimens of Opisthoplatia orientalis are sold for medicinal purposes. And many large cockroaches, such as the Madagascan hissing cockroach, are bred and kept in captivity as pets.

TAKE A COCKROACH TO LUNCH!

Despite their reputation as disgusting pests, cockroaches are used as food by humans. Those daring enough to try adult cockroaches have said that they taste like shrimp. The Aborigines of Australia and the Lao Hill tribe of Thailand eat them raw, while children throughout Laos collect the egg capsules for frying. In the United States cockroaches are never on the menu, but they still occasionally wind up on our plates, accidentally served up from kitchens that have fallen behind in their pest control efforts.

CONSERVATION STATUS

No species of cockroaches are officially endangered. The greatest threat to wild cockroaches is the destruction of their habitats, especially tropical species that have a very limited geographic range or live in small, specialized habitats. At least one species, the Russian steppe cockroach (Ectobius duskei), has become extinct because the continual expansion of cultivated wheat completely replaced its habitat.

MADEIRA COCKROACH (Rhyparobia maderae): SPECIES ACCOUNTS

Physical characteristics: Adults range in length from 1.57 to 1.97 inches (39.9 to 50 millimeters). Males and females are very similar in appearance. Their bodies are pale brown to tan. The forewings are fully developed and cover the entire body. Each forewing has two black lines at the base, while the rest of the wings have small spots.

Geographic range: This species is native to West Africa but is now found throughout the tropical regions of the world and is especially common on the islands of the Caribbean. In 1950 it became established in basements of some buildings in New York City but has spread little since then.

Habitat: The Madeira cockroach infests food stores indoors, but outdoors it prefers to live in sugarcane fields, as well as palms, guava, and bananas growing next to the fields.

Diet: This cockroach probably eats both plant and animal tissues. It is especially fond of bananas and grapes.

Behavior and reproduction: The Madeira cockroach lives in groups and may form large colonies. The male sometimes taps the ground or tree trunk with his midsection, possibly to attract females. During courtship the female feeds on special fluids from the male's second abdominal segment. The pair remain together for twenty to thirty minutes.

At temperatures ranging between 86 and 97°F (30 and 36°C), mated females produce their first egg capsule about twenty days after reaching maturity. Each egg capsule contains about forty eggs. The eggs take about two months to develop inside the body of the mother. The young larvae forage for food with their mother. They molt, shed their external skeletons, seven or eight times before reaching maturity. Males mature in 121 days; females require 150 days. The total life span, from egg to adult, is about two and a half years.

Madeira cockroaches and people: This species is a pest in some tropical regions, where it eats fruits intended for humans. It is also used as an experimental laboratory animal.

Conservation status: This species is not endangered or threatened. ∎

GERMAN COCKROACH (Blattella germanica): SPECIES ACCOUNTS

Physical characteristics: This species measures 0.4 to 0.5 inches (10.2 to 12.7 millimeters) in length. Males and females are fully winged and similar in appearance. Their bodies are pale yellowish brown to tan. The midsection has dark parallel stripes.

Geographic range: The German cockroach is found in association with humans around the world. It is even found in cold climates, such Greenland, Iceland, and the Canadian Arctic, where it lives indoors in homes and businesses.

Habitat: This species is a common pest in kitchens, food-storage areas, and restaurants. They are also widespread in the galleys and storerooms of ships and jetliners. In warmer climates they are found outdoors, living under houses, in trash piles, on date palms, and in city dumps. They also occur in gold mines and caves in South Africa.

Diet: German cockroaches eat almost anything that is plant or animal in origin.

Behavior: German cockroaches lives in groups and may build up large colonies if they are not controlled. For example, a four-room apartment in Texas had an infestation of mostly German cockroaches numbering between fifty thousand and one hundred thousand individuals. Despite their well-developed wings, they are poor fliers. They usually just glide down to the floor. Mature females "call" males by raising their wings to release a pheromone from a special gland near the tip of the abdomen. During courtship the female climbs on the back of the male and feeds on a fluid coming out of glands on the male's abdomen. Eventually, the male deposits a sperm packet directly into the body of the female.

German cockroaches and people: This species can be a household pest and is known to cause asthma attacks in people. It is also suspected to carry bacteria that cause disease in humans.

Conservation status: This species is not endangered or threatened. ∎

ORIENTAL COCKROACH (Blatta orientalis): SPECIES ACCOUNTS

Physical characteristics: This shiny blackish brown species measures 0.7 to 0.94 inches (18 to 23.9 millimeters) in length. The forewings of the male are short, covering only about two-thirds of the abdomen. The female's forewings form small pads that barely cover the rear of the thorax, or midsection. There are no hind wings.

Geographic range: This species is found in port cities around the world. It also is found throughout the United States, England, northern Europe, Israel, southern Australia, and southern South America.

Habitat: In buildings, oriental cockroaches are usually found on the ground floor or in the basement, but small numbers may be found up to the fifth floor. They prefer basements and cellars, service ducts, crawl spaces, and toilets and areas behind baths, sinks, radiators, ovens, and hot-water pipes. Large numbers can be seen around storm drains and other sources of water. In warmer parts of the United States, they often are seen outdoors around homes. During warm summer nights they commonly walk on sidewalks, in alleys, and along walls. They live in hollow trees and in garbage and trash dumps.

Diet: The oriental cockroach eats almost anything that is plant or animal in origin.

Behavior and reproduction: The life cycle of this species is seasonal. Although adults in some areas are seen throughout the year, they usually appear in May and June. They are very tolerant of cold conditions and are known to breed outdoors in England and southern Russia.

At temperatures between 86 and 97°F (30 and 36°C), mated females produce their first egg capsule twelve days after they reach maturity. Females produce two or three capsules in a lifetime. Each capsule contains, on average, sixteen eggs, which take forty-four days to hatch. The larvae molt eight to ten times before reaching adulthood. Raised in captivity, males require 146 days to reach maturity, while females take 165 days.

Oriental cockroaches and people: This species is considered a household pest. It often comes up through drains, and becomes trapped in sinks and tubs.

Conservation status: This species is not endangered or threatened. ∎

AMERICAN COCKROACH (Periplaneta americana): SPECIES ACCOUNTS

Physical characteristics: Adult American cockroaches measure 1.1 to 1.7 inches (28 to 43.2 millimeters) in length. The wings are fully developed in both males and females. Their bodies are reddish brown, with pale yellow margins around the edge of the midsection.

Geographic range: Originally from tropical Africa, this species is now found throughout the warmer regions of the world, accidentally distributed by sailing ships carrying goods and slaves.

Habitat: This species is seen both inside and outside human dwellings. American cockroaches prefer warm, moist habitats and are the most common species of cockroach in sewers in the United States. In tropical and subtropical areas they are found outdoors and in dumps, woodpiles, sewers, and cesspools.

Diet: The American cockroach feeds on almost all plant and animal materials and eats human waste in sewers.

Behavior and reproduction: American cockroaches live in groups and may form large colonies numbering in the millions. When threatened, they can fly short distances. Females produce a pheromone that attracts males from as far away as 98 feet (30 meters).

Under laboratory conditions, with temperatures ranging from 64 to 81°F (18 to 27°C) during winter and a maximum summer temperature of 95°F (35°C), female larvae need fifteen to sixteen months to reach adulthood, while males take about eighteen months. At higher temperatures the development time is shorter. Adult females live up to two years, producing as many as ninety egg capsules. Each capsule contains about sixteen eggs that take almost two months to hatch. The larvae molt nine to thirteen times before reaching adulthood.

American cockroaches and people: The American cockroach, along with the German cockroach, is the most common cockroach pest. American cockroaches have many kinds of microscopic organisms on and in their bodies that can cause disease in humans.

Conservation status: This species is not endangered or threatened. ∎

BROWNBANDED COCKROACH (Supella longipalpa): SPECIES ACCOUNTS

Physical characteristics: This small cockroach measures only 0.39 to 0.57 inches (9.9 to 14.5 millimeters) in length. In males the forewings completely cover the body, while those of the female seldom reach the tip of the abdomen. The forewings are reddish brown, with pale areas at the base and in the middle. The body color varies: the dark midsection often has a pale area in the center.

Geographic range: The brownbanded cockroach is probably native to Africa. It has now become widespread around the warmer, wetter regions of the world. It is usually found in association with homes and businesses.

Habitat: The brownbanded cockroach is found throughout homes: behind pictures, under picture frames, on and under furniture, in cupboards and closets, on bookshelves, inside televisions, and in showers.

Diet: Brownbanded cockroaches feed on all kinds of foods in kitchens. They often eat the glues of book bindings, wallpaper paste, and the adhesives on the backs of stamps and gummed labels.

Behavior and reproduction: This species tends to fly when it is disturbed. The female releases a pheromone that attracts the male from a distance.

At a temperature of about 86°F (30°C), larvae molt six to eight times before reaching adulthood. Both males and females take about fifty-five days to become adults. Males live for about 115 days, while females live about ninety days. The female produces her first egg capsule about ten days after reaching maturity and produces, on average, eleven capsules in six-day intervals during her lifetime. Each capsule contains about sixteen eggs, which take about forty days to hatch. The egg capsules are found throughout the home on walls and ceilings and on or near kitchen sinks, desks, tables, and bedding.

Brownbanded cockroaches and people: These cockroaches are household pests that can spread throughout homes.

Conservation status: This species is not endangered or threatened. ∎

FOR MORE INFORMATION

Books:

Gordon, David George. The Compleat Cockroach: A Comprehensive Guide to the Most Despised (and Least Understood) Creature on Earth. Berkeley, CA: Ten Speed Press, 1996.

Taylor, R. L. Butterflies in My Stomach; or, Insects in Human Nutrition. Santa Barbara, CA: Woodridge Press, 1975.

Periodicals:

Boraiko, A. A. "The Indomitable Cockroach." National Geographic 159, no. 1 (January 1981): 130–142.

Park, A. "Guess Who's Coming to Tea? Cockroaches!" Australian Geographic 18 (April–June 1990): 30–45.

Web sites:

"The Blattodea or Cockroaches." The Earthlife Web. http://www.earthlife.net/insects/blatodea.html (accessed on September 8, 2004).

"Blattodea: Cockroaches." Ecowatch. http://www.ento.csiro.au/Ecowatch/Insects_Invertebrates/blattodea.htm (accessed on September 8, 2004).

"Critter Catalog: Cockroaches." BioKids. http://www.biokids.umich.edu/critters/information/Blattaria.html (accessed on September 8, 2004).

"Madagascar Hissing Cockroaches." University of Kentucky Entomology. http://www.uky.edu/Agriculture/Entomology/entfacts/misc/ef014.htm (accessed on September 2004).